How can I measure the angle between the line and the plane? (At the point where the angle is greatest)

In my attachment, there’s 2 examples. In the second , I’ve drawn a couple of helping lines. In this case I only need to find the angle of the triangle. But also this isn’t as straight forward as it seems.

One possibility I’ve found is to rotate the triangle to align it with either top or right view, then I can make a measurement, but ideally I 'd like to know how to measure this without rotating the piece, as it is part of a bigger model.

Thanks in advance,

unaligned.3dm (164.0 KB)